Mortalin (mortalin 2) belongs to the Hsp family of heat shock proteins and is a non-heat-responsive protein. Mortalin's effect of binding to a p53 tumor suppressor protein so as to inactivate the function of activating transcription (Non-patent Document 1) and the like were discovered over time and the essential involvement of mortalin in carcinogenesis has been elucidated (e.g., Patent Document 1). Research and development concerning substances that target mortalin and suppress the effect and function thereof have been actively pursued recently. There are also high expectations that mortalin antibodies binding to mortalin can serve as anticancer agents (Non-patent Documents 2-6).
The present inventors previously found that an increased mortalin expression level is associated with carcinogenesis. Moreover, the present inventors have obtained an anti-mortalin antibody having the function of being internalized by cancer cells and have found that the antibody has the function of suppressing cancer cell proliferation. Thus, the present inventors have applied for a patent application relating to pharmaceutical compositions for cancer treatment, drug carriers, and the like using said antibody (Patent Document 1). The present inventors have further investigated in detail the epitope sequences of mortalin that are recognized by anti-mortalin antibodies, and have determined several types of common epitopes, including the common “LFGRAP” epitope sequence, which are recognized by anti-mortalin antibodies having the function of being internalized by cancer cells (Patent Document 2).
Anti-mortalin antibodies having the function of being internalized by cancer cells have anticancer effects. Accordingly, it has been expected that an anti-mortalin peptide antibody having anticancer effects stronger than those of the original antibodies could be obtained through preparation of an anti-mortalin monoclonal antibody using a peptide containing the common epitope as an immunogen. However, currently, such a peptide antibody having anticancer effect that is stronger than those of the above known antibodies has yet to be provided.